I. Field of the Invention
The present invention relates to data communications. More particularly, the present invention relates to novel and improved method and apparatus for detecting zero rate frames in a data transmission.
II. Description of the Related Art
Many modern day communications systems currently exist for transmitting data from a source device to a destination device. Among these systems, code division multiple access (CDMA) communications systems are efficient data transmission systems that employ spread spectrum techniques to utilize an entire available signal bandwidth. CDMA systems use other techniques to further enhance system capacity while providing the required level of performance. Such techniques include dynamic adjustment of the transmit power level and data transmission at a variable rate.
In CDMA systems, communication between users is conducted via one or more base stations. A first user on one mobile station communicates to a second user on a second mobile station by transmitting data on a reverse link to a base station. The base station receives the data and can route the data to another base station. The data is then transmitted on the forward link of the same base station, or a second base station, to the second mobile station. The forward link refers to transmission from the base station to the mobile station, and the reverse link refers to transmission from the mobile station to the base station.
Data transmissions for CDMA systems occur in frames of data. To enhance system capacity, the rate of each frame can be selected from one of a number of possible rates (e.g., full, half, quarter, and eight rates), depending on the amount of data to be transmitted. For some CDMA systems, transmission occurs in specified (e.g., 20 msec) time intervals, with each interval comprising a single larger (20 msec) frame or a number of smaller (5 msec) frames. Each frame can include a data transmission or no data transmission. A frame with no transmission is commonly referred to as a zero rate (or empty) frame.
The variable and zero rate frames allow the CDMA system to increase capacity by decreasing the transmit power level, and thus reducing interference, when smaller amounts or no data is present for transmission. At the receiving device, a detection scheme is necessary to detect whether a frame was received correctly (i.e., a good frame) or received in error (i.e., an erased or bad frame), or whether no transmission occurred (i.e., a zero rate or empty frame). This information may be required, for example, to adjust the transmit power level at the transmitting source to maintain a specified level of performance.
As can be seen, techniques that can accurately identify zero rate frames are highly desirable.